1. Field of the Invention
The present invention relates to an apparatus and method for measuring the thickness of an ink layer in a pixel, and more particularly, to an apparatus and method for measuring the thickness of an ink layer, which is filled in a pixel due to a printing operation, in real-time, and a method of controlling respective nozzles of an inkjet head using the same apparatus and method.
2. Description of the Related Art
An inkjet head is an apparatus that ejects very small ink droplets on a printing medium in a desired position via nozzles to form an image. The inkjet head has lately been applied to more various electronic devices, such as liquid crystal display devices (LCDs), organic light emitting display devices (OLEDs), and organic thin film transistors (OTFTs).
FIG. 1 is a diagram for explaining a method of manufacturing a color filter of an LCD using an inkjet head 50.
Referring to FIG. 1, ink droplets 60 in a predetermined color are ejected via nozzles 55 of the inkjet head 50 and filled in pixels 22 disposed on a substrate 10. Thereafter, ink is dried to form a solid ink layer 65 in the pixels 22 to a predetermined thickness. A black matrix 20 is formed on the substrate 20 and defines the pixels 22. In the manufacture of the color filter, the nozzles 55 of the inkjet head 50 may have different ejection characteristics so that different amount of ink droplets 60 may be ejected through the nozzles 55. When the nozzles 55 allow different amount of ink droplets 60 to pass therethrough, ink layers 65 are formed to different thicknesses in the pixels 22 as shown in FIG. 2, thereby greatly deteriorating the color characteristics of the LCD.
In order to uniformize the thicknesses of ink layers, the same amount of ink should be ejected via all nozzles of an inkjet head during a printing operation. Accordingly, it is necessary to control waveforms of voltages applied to the nozzles of the inkjet head. Thus, various methods have been proposed to control the nozzles of the inkjet head. For example, the mass of ink droplets ejected via a nozzle may be measured using a scale, such as a load cell. Alternatively, the volume of ink droplets ejected via the nozzle may be measured using a camera. In another method, after ink droplets ejected via a nozzle are filled in a pixel and dried, the thickness of an ink layer formed in the pixel may be measured. However, a method of measuring the mass of the ink droplets using the scale results in large measurement errors and takes much time. Also, measuring the volume of the ink droplets is difficult when the ink droplets have irregular shapes. Furthermore, since a method of measuring the thickness of the ink layer filled in the pixel involves a drying process, it takes much time to measure the thickness of the ink layer.